1. Field of the Invention
The present invention relates to a regulator.
2. Description of the Related Art
In a voltage regulator (hereinafter, referred to as “regulator”), there is a case where, due to an influence of an off-leak current flowing in an output transistor, an output voltage of the regulator increases when an output current is low and temperature is high. A regulator is known in which a circuit is added for providing the same level of current as the off-leak current of the output transistor in order to prevent the increase of the output voltage (e.g., refer to PLT 1).
FIG. 5 is a drawing illustrating an example configuration of a conventional regulator described in PLT 1. In FIG. 5, an off-leak current I proportional to an off-leak current Iout of an output transistor M501 flows in a transistor M502 according to a size ratio between the output transistor M501 and the transistor M502. For example, when a gate length of the output transistor M501 is L1, a gate width is W1, a gate length of the transistor M502 is L2, and a gate width is W2, a ratio between I and Iout is I/Iout=(W2/L2)/(W1/L1).
A current according to the ratio flows in the transistor M502. Further, the same amount of current flows in a transistor M503 as in the transistor M502, and proportional currents flow in the transistor 503 and a transistor 504 according to a ratio of transistor sizes between the transistors M503 and M504. In the above arrangement, by drawing the same level of a current as the off-leak current of the output transistor M501 into the transistor M504, it is possible to suppress an output voltage increase due to the off-leak current of the output transistor.
It should be noted that, in the above arrangement, a current flows in the transistor M504 according to the leak current of the transistor M502 regardless the level of the output current of the regulator when temperature is high. Therefore, when load of the regulator is heavy (when an output current is high), a wasteful current is consumed by a circuit for compensating an off-leak current of the output transistor M501.
FIG. 6 is a drawing illustrating another example configuration of a conventional regulator described in PLT 1. In FIG. 6, in the case where load of a regulator is light, an error amplifier circuit 502 operates in a direction for turning off the output transistor M501. At this time, according to the same operation of the error amplifier circuit 502, the transistor M505 is controlled in a direction for being turned off. With the above operations, an input of the inverter circuit 601 turns to a low level because it is drawn to a low level by a constant current circuit 602. As a result, the inverter circuit 601 turns on the transistor M506, and circuits (M502, M503, and M504) for compensating the off-leak current of the output transistor M501 operate.
On the other hand, when load of the regulator is heavy, the transistor M505 is turned on, the input of the inverter circuit 601 turns to a high level, and the transistor M506 is turned off. Because the transistor M506 is turned off, the off-leak current of the transistor M502 does not flow, and the circuits for compensating the off-leak current of the output transistor do not operate.
With the above arrangement, when load of the regulator is heavy (when an output current is high), it is possible to reduce current consumption by the circuits for compensating the off-leak current of the output transistor M501.